Problems of Engineering Seismology: article

Аnnotation: A brief overview of the currently existing ideas about the seismotectonic situation in the earth's crust of Iran, which is experiencing intense compression in the north-easterly direction as a result of the collision of the Arabian and Eurasian lithospheric plates, is carried out. The survey also involved geodetic data in the form of modern GPS measurements of horizontal surface displacements. An assessment of the stress-strain state of the Earth's crust of Iran (construction of an average focal mechanism) was carried out based on data on the totality of 945 focal mechanisms of earthquakes of average strength (4.4≤ MW ≤6.5) according to the ISC catalog, which occurred from 1975 to 2020, within 12 spatial samples. The focal mechanisms of the strongest earthquakes in the last 50 years ( MW =6.0-7.4) for one event in each of these samples are brought into consideration. The calculated parameters of the average mechanisms and focal mechanisms of strong earthquakes are compared both with each other and with the surrounding tectonic situation and the distribution of deformation velocity vectors according to GPS observations. A satisfactory correspondence has been established between all the comparable values. The differences in the type of deformation of the seismogenic layer of the Earth's crust of Iran in different regions are demonstrated. These differences are manifested in the different ratio of shear and thrust components in the reconstructed mean mechanism in different spatial samples. A similar difference is noted in the individual focal mechanisms of the strongest earthquakes. Nevertheless, it is possible to describe the observed nature of deformation of the Iranian crust within the framework of a single concept of collisional tectonics caused by the collision of the Arabian and Eurasian plates of the lithosphere in the last 5 million years.